In Situ Treatment of Target and Precursor PFAS in a Groundwater Plume Using a Permeable Barrier of Colloidal Activated Carbon

ABSTRACT

Per‐ and polyfluoroalkyl substances (PFAS), due to their pervasiveness, mobility, and recalcitrance in natural environments, pose challenges at a time when current remediation technologies are often ineffective in mitigating their environmental risks. A full‐scale colloidal activated carbon (CAC) barrier was implemented at a contaminated site with levels of PFAS over 100,000 ng/L to evaluate the technology's effectiveness in limiting PFAS migration within a natural groundwater system. A 70 m long barrier was implemented in 2023 and comprehensively monitored with 2 years of monthly groundwater sampling from more than 50 groundwater observation wells. The results of the monitoring program show that within the barrier, more than a 99.9% reduction of ∑ ₃₂ PFAS was achieved, and concentrations in many groundwater observation wells dropped below 4 ng/L. Downstream concentrations in nearly all observation points were expected to be influenced by the barrier decrease by more than 99.9%. Evidence of at least partial retention of ultrashort PFAS within the barrier was demonstrated during the monitoring period, as well as retention of non‐target precursors. The results of this study demonstrate that a CAC barrier is an effective method for mitigating the spread of PFAS in groundwater systems and that a careful characterization of hydrogeological and other site‐specific conditions is of great importance when designing a CAC barrier. These results provide strong evidence and demonstrated a methodology for full‐scale CAC barrier remediation that can effectively limit the spread of PFAS in natural groundwater systems.